This invention relates to a method for processing a vacuum switch utilizing an axial magnetic field in which a contact piece made of a copper-chromium alloy is specifically processed to improve the surface condition thereof. This invention also relates to a vacuum switch made in accordance with the method of this invention.
Vacuum switches utilizing an axial magnetic field are widely known in the art. FIG. 1 illustrates a typical construction of the conventional vacuum switch. In this construction, a vacuum vessel 1 made of a substantially tubular insulating material has two ends closed by flanges 2 and 3. A stationary electrode S and a movable electrode M are provided in opposed relation in the vessel 1, and supported by current carrying rods 4 and 5 that penetrate the flanges 2 and 3 in an air-tight manner. The stationary electrode S comprises a main electrode 6 and a coil electrode 7, while the movable electrode M comprises a main electrode 8 and a coil electrode 9. The electrodes 6, 7, 8 and 9 are basically made of copper. The current carrying rod 5 supporting the movable electrode M is driven in its axial direction by a driving device, not shown. Bellows 10 is provided for ensuring an air-tight condition during the movement of the rod 5 through the flange 3. The coil electrodes 7 and 9 produce an axial magnetic field in parallel with the arc created between the main electrodes 6 and 8 at the time of current interruption. A shield 12 is further provided in the vacuum vessel 1 for preventing deposition of metal vapor created during current interruption on the internal surface of the vessel 1, and further preventing deterioration of the insulation and ultimate damage of the vessel 1.
Both of the electrodes M and S are basically of a similar construction. FIG. 2 illustrates the movable electrode M having the main electrode 8 comprising an electrode 14 and a contact piece 13 secured to the upper surface of the electrode 14. In order to improve the impact-resisting and current interrupting capability and the fusion resisting property of the contact piece 13, various copper alloys are used for producing the contact piece 13. In the above described vacuum switch wherein an axial magnetic field is provided for preventing concentration of arc and improving the current interrupting capability, radial slits 15 are formed along the upper surface of the contact piece 13, as viewed in FIG. 2, so as to improve efficiency of the magnetic field. Furthermore, the coil electrode 9 has a portion formed into a coil which extends circumferentially in a plane perpendicular to the central axis of the current carrying rod 5 for generating the axial magnetic field.
In the above described construction of the conventional vacuum switch, the contact piece 13 made of a copper alloy tends to absorb impurities such as oxygen and hydrogen more than the remaining portions of the electrode M made of copper. Since the impurities tend to react with the copper alloy to form compounds, the impurities cannot be easily removed. Although various methods have been proposed for removing the impurities, methods utilizing glow discharge which is caused by applying a voltage across the electrodes, or utilizing an arc which is produced by passing an electric current through the electrodes are widely used. However, either of the methods requires a considerable length of time which is varied in accordance with the amount of the surface area of the contact piece. Furthermore the impurities contained in the slits 15 and nearby area cannot be removed satisfactorily even by the application of the above described methods.